Conventionally, registered vehicles in every country in the world are provided with numbers that are unique to the respective vehicles, and each vehicle is provided with number plates including such a number on its front and back sides. However, since the number of stolen vehicles has increased recently, and the number plates of such stolen vehicles can be replaced by those of other vehicles, the detection of the stolen cars has become difficult. Moreover, the cases where only number plates are stolen for criminal purposes also are increasing.
In order to solve these problems, it has been proposed to attach a sticker having vehicle information and a counterfeit-preventing function to an inner surface of a window of the vehicle. As such a sticker that is attached to a transparent object from a back side thereof so as to be observed from a front side thereof, for example, a vehicle-identifying sticker including a print layer showing vehicle information such as text information and a bar code on a support, and a self-destructive layer containing a hologram and the like formed on an upper surface of the print layer, which cannot be tampered, is proposed (for example, see Patent Document 1). This vehicle-identifying sticker is provided with a pressure-sensitive adhesive layer on the self-destructive layer side, and is attached to an object via the pressure-sensitive adhesive layer. If the thus once-attached vehicle-identifying sticker is peeled off, the self-destructive layer is destroyed, and thus the vehicle-identifying sticker cannot be reused.
In addition, as such a sticker that is attached to a transparent object from a back side thereof so as to be observed from a front side thereof, for example, a hologram sticker to be attached from a back side, in which a transparent adhesive layer, a hologram layer and a light transmission suppressing layer are laminated, is known (for example, see Patent Document 2). This light transmission suppressing layer has a dark color, and suppresses transmission of visible light toward a back surface of the hologram layer so as to enhance the visual contrast of a hologram image. Accordingly, when being observed from the transparent adhesive layer side, which is attached to the object, the hologram layer easily can be identified visually with the light transmission suppressing layer in its background. In addition, as the light transmission suppressing layer, a plastic film and the like that are colored by a dye or a pigment as appropriate can be used.
However, in the vehicle-identifying sticker of Patent Document 1 that is attached to an object, a self-destructive layer, a print layer including text information or the like and a support layer are provided in this order, when being observed from the object. Accordingly, if the support layer is shaved off by any means while the sticker is attached, the print layer can be reached. Thus, there is a problem that, if the print layer is further shaved off, and the text information or the like is modified using a means such as an ink for marker pens, subsequently, another print layer is newly formed, and the sticker can be counterfeited from its back surface side without being released.
In addition, the vehicle-identifying sticker of Patent Document 1 also has a problem that, even if the print layer is formed on the self-destructive-type film in order to avoid the above-described problem, an authenticating pattern such as a hologram used as the self-destructive layer is shielded by the print layer and thus is difficult to identify when being observed from the object. Then, since it is difficult to distinguish a sticker having a print layer including counterfeited text information or the like from the vehicle-identifying sticker of Patent Document 1 when being observed from the object, the thus counterfeited sticker is likely to be used with ease.
In addition, in the hologram sticker to be attached from a back side of Patent Document 2 that is attached onto an object, a transparent adhesive layer, a hologram layer and a light transmission suppressing layer are provided in this order, when being observed from the object. Accordingly, Patent Document 2 does not refer to forming an image such as text information, and even if an image is formed, the image is difficult to identify, because the dark-colored light transmission suppressing layer lies in its background.
Objects to which the stickers according to Patent Documents 1 and 2 are attached include a colored glass like a shaded glass for vehicles, and glasses to which a colored heat ray-shielding film and a metal-evaporated film and the like are attached. However, there is a problem that, if the sticker attached to such an object is viewed from the object side, an image printed on the sticker cannot be identified clearly due to the glass, and identification of the authenticating pattern of the hologram layer is also difficult. In addition, even if the printed surface of the sticker attached to such a glass is irradiated with light from the object side, the glass and the like prevent transmission of the light, and thus identification of the image on the printed surface of the sticker is very difficult.
Another example of the decorated retroreflective sheet includes a retroreflective sheet in which plural transparent beads are embedded on a surface of a transparent fixing layer, and an optically-transparent portion including no transparent bead is provided for the fixing layer in part (for example, see Patent Document 3). A reflective layer may be provided directly on a rear surface of the transparent beads, or may not be provided, but in both cases, a part where no transparent bead is provided is the optically-transparent portion, which can transmit light. A method for manufacturing such a retroreflective sheet includes: printing a block line portion K on a surface of a temporary fixing layer firstly; embedding the transparent beads on the surface of the temporary fixing layer except the part of the block line portion K; forming a reflective layer on the transparent beads in the temporary fixing layer by vapor deposition subsequently; disposing the fixing layer so that a surface thereof can follow the surface of the temporary fixing layer; applying pressure onto them; and then releasing the temporary fixing layer from the fixing layer, thereby transferring the transparent beads to the fixing layer, so that the optically-transparent portion including no transparent bead may be provided for the fixing layer.
In Patent Document 3, since the reflective layer is not formed except on the transparent beads, even if a print layer, a hologram or the like showing vehicle information such as text information and a bar code is provided on a surface layer side, the optically-transparent portion exists, and thus visibility thereof is poor. Moreover, in the case where it is used as a retroreflective sheet, since the reflective layer is formed directly on the rear surface of the transparent beads, it is used as an exposed lens type or an encapsulated lens type, and an air layer is required to be provided above the transparent beads. Thus there is a problem if it is used as a sticker for security. Furthermore, since the manufacturing method includes: embedding the transparent beads in the temporary fixing layer temporarily; and then transferring the transparent beads to the fixing layer by applying pressure, manufacturing processes thereof are complicated. In addition, Patent Document 3 does not refer to a method for providing opacity to the part including no transparent bead. In particular, in the case of forming an image by using a sublimable dye, the air layer is expanded and bubbled by heat that is applied while forming the image, and accordingly, the appearance of the sheet deteriorates, or a film forming the air layer is broken, thus the method is not preferable.
Patent Document 1: JP 2002-366036 A
Patent Document 2: JP 2000-206884 A
Patent Document 3: JP 2002-14212 A